Temporal motion vector derivation in shared merge region at picture boundary

ABSTRACT

The disclosure provides methods and apparatuses for video encoding/decoding. An apparatus includes processing circuitry that decodes prediction information for a coding region partially located outside a picture boundary. The processing circuitry determines whether a shared merge list is used for the coding region. Responsive to the shared merge list being used for the coding region, the processing circuitry constructs the shared merge list and reconstructs the coding region based on the shared merge list. Another apparatus includes processing circuitry that decodes prediction information for a current block and examines coding blocks of a collocated block of the current block according to an examination order. A second examined position in the examination order is one of the coding blocks located adjacent to a top-left corner of the collocated block. The processing circuitry determines a TMVP according to the examined coding blocks and reconstructs the current block based on the TMVP.

INCORPORATION BY REFERENCE

This present application claims the benefit of priority to U.S.Provisional Application No. 62/819,502, “TEMPORAL MV DERIVATION INSHARED MERGE REGION AT PICTURE BOUNDARY” filed on Mar. 15, 2019, whichis incorporated by reference herein in its entirety.

TECHNICAL FIELD

The present disclosure describes embodiments generally related to videocoding.

BACKGROUND

The background description provided herein is for the purpose ofgenerally presenting the context of the disclosure. Work of thepresently named inventors, to the extent the work is described in thisbackground section, as well as aspects of the description that may nototherwise qualify as prior art at the time of filing, are neitherexpressly nor impliedly admitted as prior art against the presentdisclosure.

Video coding and decoding can be performed using inter-pictureprediction with motion compensation. Uncompressed digital video caninclude a series of pictures, each picture having a spatial dimensionof, for example, 1920×1080 luminance samples and associated chrominancesamples. The series of pictures can have a fixed or variable picturerate (informally also known as frame rate) of, for example, 60 picturesper second or 60 Hz. Uncompressed video has significant bitraterequirements. For example, 1080p60 4:2:0 video at 8 bit per sample(1920×1080 luminance sample resolution at 60 Hz frame rate) requiresclose to 1.5 Gbit/s bandwidth. An hour of such video requires more than600 GBytes of storage space.

One purpose of video coding and decoding can be the reduction ofredundancy in the input video signal, through compression. Compressioncan help reduce the aforementioned bandwidth or storage spacerequirements, in some cases by two orders of magnitude or more. Bothlossless and lossy compression, as well as a combination thereof can beemployed. Lossless compression refers to techniques where an exact copyof the original signal can be reconstructed from the compressed originalsignal. When using lossy compression, the reconstructed signal may notbe identical to the original signal, but the distortion between originaland reconstructed signals is small enough to make the reconstructedsignal useful for the intended application. In the case of video, lossycompression is widely employed. The amount of distortion tolerateddepends on the application, for example, users of certain consumerstreaming applications may tolerate higher distortion than users oftelevision distribution applications. The compression ratio achievablecan reflect that: higher allowable/tolerable distortion can yield highercompression ratios.

A video encoder and decoder can utilize techniques from several broadcategories, including, for example, motion compensation, transform,quantization, and entropy coding.

Video codec technologies can include techniques known as intra coding.In intra coding, sample values are represented without reference tosamples or other data from previously reconstructed reference pictures.In some video codecs, the picture is spatially subdivided into blocks ofsamples. When all blocks of samples are coded in intra mode, thatpicture can be an intra picture. Intra pictures and their derivationssuch as independent decoder refresh pictures, can be used to reset thedecoder state and can, therefore, be used as the first picture in acoded video bitstream and a video session, or as a still image. Thesamples of an intra block can be exposed to a transform, and thetransform coefficients can be quantized before entropy coding. Intraprediction can be a technique that minimizes sample values in thepre-transform domain. In some cases, the smaller the DC value after atransform is, and the smaller the AC coefficients are, the fewer thebits that are required at a given quantization step size to representthe block after entropy coding.

Traditional intra coding such as known from, for example MPEG-2generation coding technologies, does not use intra prediction. However,some newer video compression technologies include techniques thatattempt, from, for example, surrounding sample data and/or metadataobtained during the encoding/decoding of spatially neighboring, andpreceding in decoding order, blocks of data. Such techniques arehenceforth called “intra prediction” techniques. Note that in at leastsome cases, intra prediction is only using reference data from thecurrent picture under reconstruction and not from reference pictures.

There can be many different forms of intra prediction. When more thanone of such techniques can be used in a given video coding technology,the technique in use can be coded in an intra prediction mode. Incertain cases, modes can have submodes and/or parameters, and those canbe coded individually or included in the mode codeword. Which codewordto use for a given mode/submode/parameter combination can have an impactin the coding efficiency gain through intra prediction, and so can theentropy coding technology used to translate the codewords into abitstream.

A certain mode of intra prediction was introduced with H.264, refined inH.265, and further refined in newer coding technologies such as jointexploration model (JEM), versatile video coding (VVC), and benchmark set(BMS). A predictor block can be formed using neighboring sample valuesbelonging to already available samples. Sample values of neighboringsamples are copied into the predictor block according to a direction. Areference to the direction in use can be coded in the bitstream or maybe predicted itself.

Referring to FIG. 1A, depicted in the lower right is a subset of ninepredictor directions known from H.265's 33 possible predictor directions(corresponding to the 33 angular modes of the 35 intra modes). The pointwhere the arrows converge (101) represents the sample being predicted.The arrows represent the direction from which the sample is beingpredicted. For example, arrow (102) indicates that sample (101) ispredicted from a sample or samples to the upper right, at a 45 degreeangle from the horizontal. Similarly, arrow (103) indicates that sample(101) is predicted from a sample or samples to the lower left of sample(101), in a 22.5 degree angle from the horizontal.

Still referring to FIG. 1A, on the top left there is depicted a squareblock (104) of 4×4 samples (indicated by a dashed, boldface line). Thesquare block (104) includes 16 samples, each labelled with an “S”, itsposition in the Y dimension (e.g., row index) and its position in the Xdimension (e.g., column index). For example, sample S21 is the secondsample in the Y dimension (from the top) and the first (from the left)sample in the X dimension. Similarly, sample S44 is the fourth sample inblock (104) in both the Y and X dimensions. As the block is 4×4 samplesin size, S44 is at the bottom right. Further shown are reference samplesthat follow a similar numbering scheme. A reference sample is labelledwith an R, its Y position (e.g., row index) and X position (columnindex) relative to block (104). In both H.264 and H.265, predictionsamples neighbor the block under reconstruction; therefore no negativevalues need to be used.

Intra picture prediction can work by copying reference sample valuesfrom the neighboring samples as appropriated by the signaled predictiondirection. For example, assume the coded video bitstream includessignaling that, for this block, indicates a prediction directionconsistent with arrow (102)—that is, samples are predicted from aprediction sample or samples to the upper right, at a 45 degree anglefrom the horizontal. In that case, samples S41, S32, S23, and S14 arepredicted from the same reference sample R05. Sample S44 is thenpredicted from reference sample R08.

In certain cases, the values of multiple reference samples may becombined, for example through interpolation, in order to calculate areference sample; especially when the directions are not evenlydivisible by 45 degrees.

The number of possible directions has increased as video codingtechnology has developed. In H.264 (year 2003), nine different directioncould be represented. That increased to 33 in H.265 (year 2013), andJEM/VVC/BMS, at the time of disclosure, can support up to 65 directions.Experiments have been conducted to identify the most likely directions,and certain techniques in the entropy coding are used to represent thoselikely directions in a small number of bits, accepting a certain penaltyfor less likely directions. Further, the directions themselves cansometimes be predicted from neighboring directions used in neighboring,already decoded, blocks.

FIG. 1B shows a schematic (105) that depicts 65 intra predictiondirections according to JEM to illustrate the increasing number ofprediction directions over time.

The mapping of intra prediction directions bits in the coded videobitstream that represent the direction can be different from videocoding technology to video coding technology; and can range, forexample, from simple direct mappings of prediction direction to intraprediction mode, to codewords, to complex adaptive schemes involvingmost probable modes, and similar techniques. In all cases, however,there can be certain directions that are statistically less likely tooccur in video content than certain other directions. As the goal ofvideo compression is the reduction of redundancy, those less likelydirections will, in a well working video coding technology, berepresented by a larger number of bits than more likely directions.

Motion compensation can be a lossy compression technique and can relateto techniques where a block of sample data from a previouslyreconstructed picture or part thereof (reference picture), after beingspatially shifted in a direction indicated by a motion vector (MVhenceforth), is used for the prediction of a newly reconstructed pictureor picture part. In some cases, the reference picture can be the same asthe picture currently under reconstruction. MVs can have two dimensionsX and Y, or three dimensions, the third being an indication of thereference picture in use (the latter, indirectly, can be a timedimension).

In some video compression techniques, an MV applicable to a certain areaof sample data can be predicted from other MVs, for example from thoserelated to another area of sample data spatially adjacent to the areaunder reconstruction, and preceding that MV in decoding order. Doing socan substantially reduce the amount of data required for coding the MV,thereby removing redundancy and increasing compression. MV predictioncan work effectively, for example, because when coding an input videosignal derived from a camera (known as natural video) there is astatistical likelihood that areas larger than the area to which a singleMV is applicable move in a similar direction and, therefore, can in somecases be predicted using a similar motion vector derived from MVs ofneighboring area. That results in the MV found for a given area to besimilar or the same as the MV predicted from the surrounding MVs, andthat in turn can be represented, after entropy coding, in a smallernumber of bits than what would be used if coding the MV directly. Insome cases, MV prediction can be an example of lossless compression of asignal (namely: the MVs) derived from the original signal (namely: thesample stream). In other cases, MV prediction itself can be lossy, forexample because of rounding errors when calculating a predictor fromseveral surrounding MVs.

Various MV prediction mechanisms are described in H.265/HEVC (ITU-T Rec.H.265, “High Efficiency Video Coding”, December 2016). Out of the manyMV prediction mechanisms that H.265 offers, advanced motion vectorprediction (AMVP) mode and merge mode are described here.

In AMVP mode, motion information of spatial and temporal neighboringblocks of a current block can be used to predict motion information ofthe current block, while the prediction residue is further coded.Examples of spatial and temporal neighboring candidates are shown inFIG. 1C and FIG. 1D, respectively. A two-candidate motion vectorpredictor list is formed. The first candidate predictor is from thefirst available motion vector of the two blocks A0 (112), A1 (113)adjacent the bottom-left corner of the current block (111), as shown inFIG. 1C. The second candidate predictor is from the first availablemotion vector of the three blocks B0 (114), B1 (115), and B2 (116) abovethe current block (111). If no valid motion vector can be found from thechecked locations, no candidate will be filled in the list. If twoavailable candidates have the same motion information, only onecandidate will be kept in the list. If the list is not full, i.e., thelist does not have two different candidates, a temporal collocatedmotion vector (after scaling) from C0 (122) adjacent the bottom-rightcorner of a collocated block (121) in a reference picture will be usedas another candidate, as shown in FIG. 1D. If motion information at C0(122) location is not available, the center location C1 (123) of thecollocated block in the reference picture will be used instead. In theabove derivation, if there are still not enough motion vector predictorcandidates, a zero motion vector will be used to fill up the list. Twoflags mvp_10_flag and mvp_11_flag are signaled in the bitstream toindicate the AMVP index (0 or 1) for MV candidate list L0 and L1,respectively.

In a merge mode for inter-picture prediction, if a merge flag (includinga skip flag) is signaled as TRUE, a merge index is then signaled toindicate which candidate in a merge candidate list will be used toindicate the motion vectors of the current block. At the decoder, themerge candidate list is constructed based on spatial and temporalneighbors of the current block. As shown in FIG. 1C, up to four MVsderived from five spatial neighboring blocks (A0-B2) are added into themerge candidate list. In addition, as shown in FIG. 1D, up to one MVfrom two locations (C0 and C1) in the collocated block of the referencepicture is added to the list. Additional merge candidates includecombined bi-predictive candidates and zero motion vector candidates,etc. Before taking the motion information of a block as a mergecandidate, redundancy checks are performed to check whether it isidentical to an element in the current merge candidate list. If it isdifferent from each element in the current merge candidate list, it willbe added to the merge candidate list as a merge candidate.MaxMergeCandsNum is defined as the size of the merge candidate list interms of candidate number. In HEVC, MaxMergeCandsNum is signaled in thebitstream. A skip mode can be considered as a special merge mode withzero residual.

SUMMARY

Aspects of the disclosure provide methods and apparatuses for videoencoding/decoding. In some examples, an apparatus for video decodingincludes receiving circuitry and processing circuitry.

The processing circuitry decodes prediction information for a codingregion that is partially located outside a picture boundary in a currentpicture that is a part of a coded video sequence. The processingcircuitry determines whether a shared merge list is used for the codingregion. Responsive to the shared merge list being used for the codingregion, the processing circuitry constructs the shared merge list andreconstructs the coding region based on the shared merge list.

In an embodiment, the shared merge list is determined to be used for thecoding region when a size of the coding region is equal to or smallerthan a first size threshold.

In another embodiment, the coding region includes a plurality of codingblocks and the shared merge list is determined to be used for the codingregion when: (i) a size of the coding region is equal to or larger thana second size threshold; and (ii) a block size of one of the codingblocks is smaller than the second size threshold.

The processing circuitry can select a first block that is locatedadjacent a center position of a collocated region of the coding region.The collocated region is in a reference picture of the coding region.The processing circuitry determines whether the first block is locatedinside the picture boundary of the current picture and is coded in aninter prediction mode. When the first block is determined to be locatedinside the picture boundary of the current picture and to be coded inthe inter prediction mode, the processing circuitry constructs theshared merge list based on the first block.

In another embodiment, the processing circuitry selects a second blockthat is located adjacent a top-left position of the collocated region ofthe current region. The processing circuitry determines whether thesecond block is coded in an inter prediction mode. When the second blockis determined to be coded in the inter prediction mode, the processingcircuitry constructs the shared merge list based on the second block.

The disclosure also presents another apparatus for video decoding. Theapparatus includes processing circuitry that decodes predictioninformation for a current block in a current picture that is a part of acoded video sequence. The prediction information indicates a merge modefor the current block. The processing circuitry examines a plurality ofcoding blocks of a collocated block of the current block according to anexamination order. A second examined position in the examination orderis one of the coding blocks that is located adjacent to a top-leftcorner of the collocated block. The collocated block is in a referencepicture of the current block. The processing circuitry determines atemporal motion vector predictor (TMVP) according to the examined codingblocks and reconstructs the current block based on the TMVP.

In an embodiment, the processing circuitry selects one of the codingblocks according to the examination order and determines whether theselected coding block is coded in an inter prediction mode. For example,a coding block that is located adjacent the top-left corner of thecollocated block can be examined after a coding block that is locatedadjacent a bottom-right corner of the collocated block, according to theexamination order.

Aspects of the disclosure also provide a non-transitorycomputer-readable medium storing instructions which when executed by acomputer for video decoding cause the computer to perform any one of acombination of the methods for video decoding.

BRIEF DESCRIPTION OF THE DRAWINGS

Further features, the nature, and various advantages of the disclosedsubject matter will be more apparent from the following detaileddescription and the accompanying drawings in which:

FIG. 1A is a schematic illustration of an exemplary subset of intraprediction modes;

FIG. 1B is an illustration of exemplary intra prediction directions;

FIG. 1C is a schematic illustration of a current block and itssurrounding spatial merge candidates in one example;

FIG. 1D is a schematic illustration of a collocated block and temporalmerge candidates in one example;

FIG. 2 is a schematic illustration of a simplified block diagram of acommunication system in accordance with an exemplary embodiment;

FIG. 3 is a schematic illustration of a simplified block diagram of acommunication system in accordance with an exemplary embodiment;

FIG. 4 is a schematic illustration of a simplified block diagram of adecoder in accordance with an exemplary embodiment;

FIG. 5 is a schematic illustration of a simplified block diagram of anencoder in accordance with an exemplary embodiment;

FIG. 6 shows a block diagram of an encoder in accordance with anotherexemplary embodiment;

FIG. 7 shows a block diagram of a decoder in accordance with anotherexemplary embodiment;

FIG. 8 shows four examples of merge sharing nodes according to exemplaryembodiments of the disclosure;

FIG. 9 shows an example of a difference between Type-1 and Type-2definitions according to an exemplary embodiment of the disclosure;

FIG. 10 shows a schematic illustration of a collocated block andtemporal merge candidates according to an embodiment of the disclosure;

FIG. 11 shows a flow chart outlining an exemplary process according toan embodiment of the disclosure;

FIG. 12 shows a flow chart outlining an exemplary process according toanother embodiment of the disclosure; and

FIG. 13 is a schematic illustration of a computer system in accordancewith an exemplary embodiment.

DETAILED DESCRIPTION OF EMBODIMENTS

FIG. 2 illustrates a simplified block diagram of a communication system(200) according to an exemplary embodiment of the present disclosure.The communication system (200) includes a plurality of terminal devicesthat can communicate with each other, via, for example, a network (250).For example, the communication system (200) includes a first pair ofterminal devices (210) and (220) interconnected via the network (250).In the FIG. 2 example, the first pair of terminal devices (210) and(220) performs unidirectional transmission of data. For example, theterminal device (210) may code video data (e.g., a stream of videopictures that are captured by the terminal device (210)) fortransmission to the other terminal device (220) via the network (250).The encoded video data can be transmitted in the form of one or morecoded video bitstreams. The terminal device (220) may receive the codedvideo data from the network (250), decode the coded video data torecover the video pictures and display video pictures according to therecovered video data. Unidirectional data transmission may be common inmedia serving applications and the like.

In another example, the communication system (200) includes a secondpair of terminal devices (230) and (240) that performs bidirectionaltransmission of coded video data that may occur, for example, duringvideoconferencing. For bidirectional transmission of data, in anexample, each terminal device of the terminal devices (230) and (240)may code video data (e.g., a stream of video pictures that are capturedby the terminal device) for transmission to the other terminal device ofthe terminal devices (230) and (240) via the network (250). Eachterminal device of the terminal devices (230) and (240) also may receivethe coded video data transmitted by the other terminal device of theterminal devices (230) and (240), and may decode the coded video data torecover the video pictures and may display video pictures at anaccessible display device according to the recovered video data.

In the FIG. 2 example, the terminal devices (210), (220), (230) and(240) may be illustrated as servers, personal computers and smartphones, but the principles of the present disclosure may be not solimited. Embodiments of the present disclosure can also find applicationwith laptop computers, tablet computers, media players, dedicated videoconferencing equipment, and the like. The network (250) represents anynumber of networks that convey coded video data among the terminaldevices (210), (220), (230) and (240), including for example wireline(wired) and/or wireless communication networks. The communicationnetwork (250) may exchange data in circuit-switched and/orpacket-switched channels. Representative networks includetelecommunications networks, local area networks, wide area networksand/or the Internet. For the purposes of the present discussion, thearchitecture and topology of the network (250) may be immaterial to theoperation of the present disclosure unless explained herein below.

FIG. 3 illustrates, as an example for an application for the disclosedsubject matter, the placement of a video encoder and a video decoder ina streaming environment. The disclosed subject matter can be equallyapplicable to other video enabled applications, including, for example,video conferencing, digital TV, storing of compressed video on digitalmedia including CD, DVD, memory stick, and the like.

A streaming system may include a capture subsystem (313) that caninclude a video source (301), for example a digital camera, creating forexample a stream of video pictures (302) that are uncompressed. In anexample, the stream of video pictures (302) includes samples that aretaken by the digital camera. The stream of video pictures (302),depicted as a bold line to emphasize a high data volume when compared toencoded video data (304) (or coded video bitstreams), can be processedby an electronic device (320) that includes a video encoder (303)coupled to the video source (301). The video encoder (303) can includehardware, software, or a combination thereof to enable or implementaspects of the disclosed subject matter as described in more detailbelow. The encoded video data (304) (or encoded video bitstream (304)),depicted as a thin line to emphasize the lower data volume when comparedto the stream of video pictures (302), can be stored on a streamingserver (305) for future use. One or more streaming client subsystems,such as client subsystems (306) and (308) in FIG. 3 can access thestreaming server (305) to retrieve copies (307) and (309) of the encodedvideo data (304). A client subsystem (306) can include a video decoder(310), for example, in an electronic device (330). The video decoder(310) decodes the incoming copy (307) of the encoded video data andcreates an outgoing stream of video pictures (311) that can be renderedon a display (312) (e.g., display screen) or other rendering device (notdepicted). In some streaming systems, the encoded video data (304),(307), and (309) (e.g., video bitstreams) can be encoded according tocertain video coding/compression standards. Examples of those standardsinclude ITU-T Recommendation H.265. In an example, a video codingstandard under development is informally known as Versatile Video Coding(VVC). The disclosed subject matter may be used in the context of VVC.

It is noted that the electronic devices (320) and (330) can includeother components (not shown). For example, the electronic device (320)can include a video decoder (not shown) and the electronic device (330)can include a video encoder (not shown) as well.

FIG. 4 shows a block diagram of a video decoder (410) according to anembodiment of the present disclosure. The video decoder (410) can beincluded in an electronic device (430). The electronic device (430) caninclude a receiver (431) (e.g., receiving circuitry). The video decoder(410) can be used in the place of the video decoder (310) in the FIG. 3example.

The receiver (431) may receive one or more coded video sequences to bedecoded by the video decoder (410); in the same or another embodiment,one coded video sequence at a time, where the decoding of each codedvideo sequence is independent from other coded video sequences. Thecoded video sequence may be received from a channel (401), which may bea hardware/software link to a storage device which stores the encodedvideo data. The receiver (431) may receive the encoded video data withother data, for example, coded audio data and/or ancillary data streams,that may be forwarded to their respective using entities (not depicted).The receiver (431) may separate the coded video sequence from the otherdata. To combat network jitter, a buffer memory (415) may be coupled inbetween the receiver (431) and an entropy decoder/parser (420) (“parser(420)” henceforth). In certain applications, the buffer memory (415) ispart of the video decoder (410). In others, it can be outside of thevideo decoder (410) (not depicted). In still others, there can be abuffer memory (not depicted) outside of the video decoder (410), forexample to combat network jitter, and in addition another buffer memory(415) inside the video decoder (410), for example to handle playouttiming. When the receiver (431) is receiving data from a store/forwarddevice of sufficient bandwidth and controllability, or from anisosynchronous network, the buffer memory (415) may not be needed, orcan be small. For use on best effort packet networks such as theInternet, the buffer memory (415) may be required, can be comparativelylarge and can be advantageously of adaptive size, and may at leastpartially be implemented in an operating system or similar elements (notdepicted) outside of the video decoder (410).

The video decoder (410) may include the parser (420) to reconstructsymbols (421) from the coded video sequence. Categories of those symbolsinclude information used to manage operation of the video decoder (410),and potentially information to control a rendering device such as arender device (412) (e.g., a display screen) that is not an integralpart of the electronic device (430) but can be coupled to the electronicdevice (430), as was shown in FIG. 4. The control information for therendering device(s) may be in the form of Supplemental EnhancementInformation (SEI messages) or Video Usability Information (VUI)parameter set fragments (not depicted). The parser (420) mayparse/entropy-decode the coded video sequence that is received. Thecoding of the coded video sequence can be in accordance with a videocoding technology or standard, and can follow various principles,including variable length coding. Huffman coding, arithmetic coding withor without context sensitivity, and so forth. The parser (420) mayextract from the coded video sequence, a set of subgroup parameters forat least one of the subgroups of pixels in the video decoder, based uponat least one parameter corresponding to the group. Subgroups can includeGroups of Pictures (GOPs), pictures, tiles, slices, macroblocks, CodingUnits (CUs), blocks, Transform Units (TUs), Prediction Units (PUs) andso forth. The parser (420) may also extract from the coded videosequence information such as transform coefficients, quantizer parametervalues, motion vectors, and so forth.

The parser (420) may perform an entropy decoding/parsing operation onthe video sequence received from the buffer memory (415), so as tocreate symbols (421).

Reconstruction of the symbols (421) can involve multiple different unitsdepending on the type of the coded video picture or parts thereof (suchas: inter and intra picture, inter and intra block), and other factors.Which units are involved, and how, can be controlled by the subgroupcontrol information that was parsed from the coded video sequence by theparser (420). The flow of such subgroup control information between theparser (420) and the multiple units below is not depicted for clarity.

Beyond the functional blocks already mentioned, the video decoder (410)can be conceptually subdivided into a number of functional units asdescribed below. In a practical implementation operating undercommercial constraints, many of these units interact closely with eachother and can, at least partly, be integrated into each other. However,for the purpose of describing the disclosed subject matter, theconceptual subdivision into the functional units below is appropriate.

A first unit is the scaler/inverse transform unit (451). Thescaler/inverse transform unit (451) receives a quantized transformcoefficient as well as control information, including which transform touse, block size, quantization factor, quantization scaling matrices,etc. as symbol(s) (421) from the parser (420). The scaler/inversetransform unit (451) can output blocks comprising sample values that canbe input into aggregator (455).

In some cases, the output samples of the scaler/inverse transform (451)can pertain to an intra coded block; that is: a block that is not usingpredictive information from previously reconstructed pictures, but canuse predictive information from previously reconstructed parts of thecurrent picture. Such predictive information can be provided by an intrapicture prediction unit (452). In some cases, the intra pictureprediction unit (452) generates a block of the same size and shape ofthe block under reconstruction, using surrounding already reconstructedinformation fetched from the current picture buffer (458). The currentpicture buffer (458) buffers, for example, partly reconstructed currentpicture and/or fully reconstructed current picture. The aggregator(455), in some cases, adds, on a per sample basis, the predictioninformation that the intra prediction unit (452) has generated to theoutput sample information as provided by the scaler/inverse transformunit (451).

In other cases, the output samples of the scaler/inverse transform unit(451) can pertain to an inter coded, and potentially motion compensatedblock. In such a case, a motion compensation prediction unit (453) canaccess reference picture memory (457) to fetch samples used forprediction. After motion compensating the fetched samples in accordancewith the symbols (421) pertaining to the block, these samples can beadded by the aggregator (455) to the output of the scaler/inversetransform unit (451) (in this case called the residual samples orresidual signal) so as to generate output sample information. Theaddresses within the reference picture memory (457) from where themotion compensation prediction unit (453) fetches prediction samples canbe controlled by motion vectors, available to the motion compensationprediction unit (453) in the form of symbols (421) that can have, forexample X, Y, and reference picture components. Motion compensation alsocan include interpolation of sample values as fetched from the referencepicture memory (457) when sub-sample exact motion vectors are in use,motion vector prediction mechanisms, and so forth.

The output samples of the aggregator (455) can be subject to variousloop filtering techniques in the loop filter unit (456). Videocompression technologies can include in-loop filter technologies thatare controlled by parameters included in the coded video sequence (alsoreferred to as coded video bitstream) and made available to the loopfilter unit (456) as symbols (421) from the parser (420), but can alsobe responsive to meta-information obtained during the decoding ofprevious (in decoding order) parts of the coded picture or coded videosequence, as well as responsive to previously reconstructed andloop-filtered sample values.

The output of the loop filter unit (456) can be a sample stream that canbe output to the render device (412) as well as stored in the referencepicture memory (457) for use in future inter-picture prediction.

Certain coded pictures, once fully reconstructed, can be used asreference pictures for future prediction. For example, once a codedpicture corresponding to a current picture is fully reconstructed andthe coded picture has been identified as a reference picture (by, forexample, the parser (420)), the current picture buffer (458) can becomea part of the reference picture memory (457), and a fresh currentpicture buffer can be reallocated before commencing the reconstructionof the following coded picture.

The video decoder (410) may perform decoding operations according to apredetermined video compression technology in a standard, such as ITU-TRec. H.265. The coded video sequence may conform to a syntax specifiedby the video compression technology or standard being used, in the sensethat the coded video sequence adheres to both the syntax of the videocompression technology or standard and the profiles as documented in thevideo compression technology or standard. Specifically, a profile canselect certain tools as the only tools available for use under thatprofile from all the tools available in the video compression technologyor standard. Also necessary for compliance can be that the complexity ofthe coded video sequence is within bounds as defined by the level of thevideo compression technology or standard. In some cases, levels restrictthe maximum picture size, maximum frame rate, maximum reconstructionsample rate (measured in, for example megasamples per second), maximumreference picture size, and so on. Limits set by levels can, in somecases, be further restricted through Hypothetical Reference Decoder(HRD) specifications and metadata for HRD buffer management signaled inthe coded video sequence.

In an embodiment, the receiver (431) may receive additional (redundant)data with the encoded video. The additional data may be included as partof the coded video sequence(s). The additional data may be used by thevideo decoder (410) to properly decode the data and/or to moreaccurately reconstruct the original video data. Additional data can bein the form of, for example, temporal, spatial, or signal noise ratio(SNR) enhancement layers, redundant slices, redundant pictures, forwarderror correction codes, and so on.

FIG. 5 shows a block diagram of a video encoder (503) according to anembodiment of the present disclosure. The video encoder (503) isincluded in an electronic device (520). The electronic device (520)includes a transmitter (540) (e.g., transmitting circuitry). The videoencoder (503) can be used in the place of the video encoder (303) in theFIG. 3 example.

The video encoder (503) may receive video samples from a video source(501) (that is not part of the electronic device (520) in the FIG. 5example) that may capture video image(s) to be coded by the videoencoder (503). In another example, the video source (501) is a part ofthe electronic device (520).

The video source (501) may provide the source video sequence to be codedby the video encoder (503) in the form of a digital video sample streamthat can be of any suitable bit depth (for example: 8 bit, 10 bit, 12bit, . . . ), any colorspace (for example, BT.601 Y CrCB, RGB, . . . ),and any suitable sampling structure (for example Y CrCb 4:2:0, Y CrCb4:4:4). In a media serving system, the video source (501) may be astorage device storing previously prepared video. In a videoconferencingsystem, the video source (501) may be a camera that captures local imageinformation as a video sequence. Video data may be provided as aplurality of individual pictures that impart motion when viewed insequence. The pictures themselves may be organized as a spatial array ofpixels, wherein each pixel can comprise one or more samples depending onthe sampling structure, color space, etc. in use. A person skilled inthe art can readily understand the relationship between pixels andsamples. The description below focuses on samples.

According to an embodiment, the video encoder (503) may code andcompress the pictures of the source video sequence into a coded videosequence (543) in real time or under any other time constraints asrequired by the application. Enforcing appropriate coding speed is onefunction of a controller (550). In some embodiments, the controller(550) controls other functional units as described below and isfunctionally coupled to the other functional units. The coupling is notdepicted for clarity. Parameters set by the controller (550) can includerate control related parameters (picture skip, quantizer, lambda valueof rate-distortion optimization techniques, . . . ), picture size, groupof pictures (GOP) layout, maximum motion vector allowed reference area,and so forth. The controller (550) can be configured to have othersuitable functions that pertain to the video encoder (503) optimized fora certain system design.

In some embodiments, the video encoder (503) is configured to operate ina coding loop. As an oversimplified description, in an example, thecoding loop can include a source coder (530) (e.g., responsible forcreating symbols, such as a symbol stream, based on an input picture tobe coded, and a reference picture(s)), and a (local) decoder (533)embedded in the video encoder (503). The decoder (533) reconstructs thesymbols to create the sample data in a similar manner as a (remote)decoder also would create (as any compression between symbols and codedvideo bitstream is lossless in the video compression technologiesconsidered in the disclosed subject matter). The reconstructed samplestream (sample data) is input to the reference picture memory (534). Asthe decoding of a symbol stream leads to bit-exact results independentof decoder location (local or remote), the content in the referencepicture memory (534) is also bit exact between the local encoder andremote encoder. In other words, the prediction part of an encoder “sees”as reference picture samples exactly the same sample values as a decoderwould “see” when using prediction during decoding. This fundamentalprinciple of reference picture synchronicity (and resulting drift, ifsynchronicity cannot be maintained, for example because of channelerrors) is used in some related arts as well.

The operation of the “local” decoder (533) can be the same as of a“remote” decoder, such as the video decoder (410), which has alreadybeen described in detail above in conjunction with FIG. 4. Brieflyreferring also to FIG. 4, however, as symbols are available andencoding/decoding of symbols to a coded video sequence by an entropycoder (545) and the parser (420) can be lossless, the entropy decodingparts of the video decoder (410), including the buffer memory (415) andthe parser (420) may not be fully implemented in the local decoder(533).

An observation that can be made at this point is that any decodertechnology except the parsing/entropy decoding that is present in adecoder also necessarily needs to be present, in substantially identicalfunctional form, in a corresponding encoder. For this reason, thedisclosed subject matter focuses on decoder operation. The descriptionof encoder technologies can be abbreviated as they are the inverse ofthe comprehensively described decoder technologies. Only in certainareas a more detail description is required and provided below.

During operation, in some examples, the source coder (530) may performmotion compensated predictive coding, which codes an input picturepredictively with reference to one or more previously-coded picture fromthe video sequence that were designated as “reference pictures”. In thismanner, the coding engine (532) codes differences between pixel blocksof an input picture and pixel blocks of reference picture(s) that may beselected as prediction reference(s) to the input picture.

The local video decoder (533) may decode coded video data of picturesthat may be designated as reference pictures, based on symbols createdby the source coder (530). Operations of the coding engine (532) mayadvantageously be lossy processes. When the coded video data may bedecoded at a video decoder (not shown in FIG. 5), the reconstructedvideo sequence typically may be a replica of the source video sequencewith some errors. The local video decoder (533) replicates decodingprocesses that may be performed by the video decoder on referencepictures and may cause reconstructed reference pictures to be stored inthe reference picture cache (534). In this manner, the video encoder(503) may store copies of reconstructed reference pictures locally thathave common content as the reconstructed reference pictures that will beobtained by a far-end video decoder (absent transmission errors).

The predictor (535) may perform prediction searches for the codingengine (532). That is, for a new picture to be coded, the predictor(535) may search the reference picture memory (534) for sample data (ascandidate reference pixel blocks) or certain metadata such as referencepicture motion vectors, block shapes, and so on, that may serve as anappropriate prediction reference for the new pictures. The predictor(535) may operate on a sample block-by-pixel block basis to findappropriate prediction references. In some cases, as determined bysearch results obtained by the predictor (535), an input picture mayhave prediction references drawn from multiple reference pictures storedin the reference picture memory (534).

The controller (550) may manage coding operations of the source coder(530), including, for example, setting of parameters and subgroupparameters used for encoding the video data.

Output of all aforementioned functional units may be subjected toentropy coding in the entropy coder (545). The entropy coder (545)translates the symbols as generated by the various functional units intoa coded video sequence, by lossless compressing the symbols according totechnologies such as Huffman coding, variable length coding, arithmeticcoding, and so forth.

The transmitter (540) may buffer the coded video sequence(s) as createdby the entropy coder (545) to prepare for transmission via acommunication channel (560), which may be a hardware/software link to astorage device which would store the encoded video data. The transmitter(540) may merge coded video data from the video coder (503) with otherdata to be transmitted, for example, coded audio data and/or ancillarydata streams (sources not shown).

The controller (550) may manage operation of the video encoder (503).During coding, the controller (550) may assign to each coded picture acertain coded picture type, which may affect the coding techniques thatmay be applied to the respective picture. For example, pictures oftenmay be assigned as one of the following picture types:

An Intra Picture (I picture) may be one that may be coded and decodedwithout using any other picture in the sequence as a source ofprediction. Some video codecs allow for different types of intrapictures, including, for example Independent Decoder Refresh (“IDR”)Pictures. A person skilled in the art is aware of those variants of Ipictures and their respective applications and features.

A predictive picture (P picture) may be one that may be coded anddecoded using intra prediction or inter prediction using at most onemotion vector and reference index to predict the sample values of eachblock.

A bi-directionally predictive picture (B Picture) may be one that may becoded and decoded using intra prediction or inter prediction using atmost two motion vectors and reference indices to predict the samplevalues of each block. Similarly, multiple-predictive pictures can usemore than two reference pictures and associated metadata for thereconstruction of a single block.

Source pictures commonly may be subdivided spatially into a plurality ofsample blocks (for example, blocks of 4×4, 8×8, 4×8, or 16×16 sampleseach) and coded on a block-by-block basis. Blocks may be codedpredictively with reference to other (already coded) blocks asdetermined by the coding assignment applied to the blocks' respectivepictures. For example, blocks of I pictures may be codednon-predictively or they may be coded predictively with reference toalready coded blocks of the same picture (spatial prediction or intraprediction). Pixel blocks of P pictures may be coded predictively, viaspatial prediction or via temporal prediction with reference to onepreviously coded reference picture. Blocks of B pictures may be codedpredictively, via spatial prediction or via temporal prediction withreference to one or two previously coded reference pictures.

The video encoder (503) may perform coding operations according to apredetermined video coding technology or standard, such as ITU-T Rec.H.265. In its operation, the video encoder (503) may perform variouscompression operations, including predictive coding operations thatexploit temporal and spatial redundancies in the input video sequence.The coded video data, therefore, may conform to a syntax specified bythe video coding technology or standard being used.

In an embodiment, the transmitter (540) may transmit additional datawith the encoded video. The source coder (530) may include such data aspart of the coded video sequence. Additional data may comprisetemporal/spatial/SNR enhancement layers, other forms of redundant datasuch as redundant pictures and slices, SEI messages, VUI parameter setfragments, and so on.

A video may be captured as a plurality of source pictures (videopictures) in a temporal sequence. Intra-picture prediction (oftenabbreviated to intra prediction) makes use of spatial correlation in agiven picture, and inter-picture prediction makes uses of the (temporalor other) correlation between the pictures. In an example, a specificpicture under encoding/decoding, which is referred to as a currentpicture, is partitioned into blocks. When a block in the current pictureis similar to a reference block in a previously coded and still bufferedreference picture in the video, the block in the current picture can becoded by a vector that is referred to as a motion vector. The motionvector points to the reference block in the reference picture, and canhave a third dimension identifying the reference picture, in casemultiple reference pictures are in use.

In some embodiments, a bi-prediction technique can be used in theinter-picture prediction. According to the bi-prediction technique, tworeference pictures, such as a first reference picture and a secondreference picture that are both prior in decoding order to the currentpicture in the video (but may be in the past and future, respectively,in display order) are used. A block in the current picture can be codedby a first motion vector that points to a first reference block in thefirst reference picture, and a second motion vector that points to asecond reference block in the second reference picture. The block can bepredicted by a combination of the first reference block and the secondreference block.

Further, a merge mode technique can be used in the inter-pictureprediction to improve coding efficiency.

According to some embodiments of the disclosure, predictions, such asinter-picture predictions and intra-picture predictions are performed inthe unit of blocks. For example, according to the HEVC standard, apicture in a sequence of video pictures is partitioned into coding treeunits (CTU) for compression, the CTUs in a picture have the same size,such as 64×64 pixels, 32×32 pixels, or 16×16 pixels. In general, a CTUincludes three coding tree blocks (CTBs), which are one luma CTB and twochroma CTBs. Each CTU can be recursively quad-tree split into one ormultiple coding units (CUs). For example, a CTU of 64×64 pixels can besplit into one CU of 64×64 pixels, or 4 CUs of 32×32 pixels, or 16 CUsof 16×16 pixels. In an example, each CU is analyzed to determine aprediction type for the CU, such as an inter prediction type or an intraprediction type. The CU is split into one or more prediction units (PUs)depending on the temporal and/or spatial predictability. Generally, eachPU includes a luma prediction block (PB), and two chroma PBs. In anembodiment, a prediction operation in coding (encoding/decoding) isperformed in the unit of a prediction block. Using a luma predictionblock as an example of a prediction block, the prediction block includesa matrix of values (e.g., luma values) for pixels, such as 8×8 pixels,16×16 pixels, 8×16 pixels, 16×8 pixels, and the like.

FIG. 6 shows a diagram of a video encoder (603) according to anotherembodiment of the disclosure. The video encoder (603) is configured toreceive a processing block (e.g., a prediction block) of sample valueswithin a current video picture in a sequence of video pictures, andencode the processing block into a coded picture that is part of a codedvideo sequence. In an example, the video encoder (603) is used in theplace of the video encoder (303) in the FIG. 3 example.

In an HEVC example, the video encoder (603) receives a matrix of samplevalues for a processing block, such as a prediction block of 8×8samples, and the like. The video encoder (603) determines whether theprocessing block is best coded using intra mode, inter mode, orbi-prediction mode using, for example, rate-distortion optimization.When the processing block is to be coded in intra mode, the videoencoder (603) may use an intra prediction technique to encode theprocessing block into the coded picture; and when the processing blockis to be coded in inter mode or bi-prediction mode, the video encoder(603) may use an inter prediction or bi-prediction technique,respectively, to encode the processing block into the coded picture. Incertain video coding technologies, merge mode can be an inter pictureprediction submode where the motion vector is derived from one or moremotion vector predictors without the benefit of a coded motion vectorcomponent outside the predictors. In certain other video codingtechnologies, a motion vector component applicable to the subject blockmay be present. In an example, the video encoder (603) includes othercomponents, such as a mode decision module (not shown) to determine themode of the processing blocks.

In the FIG. 6 example, the video encoder (603) includes the interencoder (630), an intra encoder (622), a residue calculator (623), aswitch (626), a residue encoder (624), a general controller (621), andan entropy encoder (625) coupled together as shown in FIG. 6.

The inter encoder (630) is configured to receive the samples of thecurrent block (e.g., a processing block), compare the block to one ormore reference blocks in reference pictures (e.g., blocks in previouspictures and later pictures), generate inter prediction information(e.g., description of redundant information according to inter encodingtechnique, motion vectors, merge mode information), and calculate interprediction results (e.g., predicted block) based on the inter predictioninformation using any suitable technique. In some examples, thereference pictures are decoded reference pictures that are decoded basedon the encoded video information.

The intra encoder (622) is configured to receive the samples of thecurrent block (e.g., a processing block), in some cases compare theblock to blocks already coded in the same picture, generate quantizedcoefficients after transform, and in some cases also intra predictioninformation (e.g., an intra prediction direction information accordingto one or more intra encoding techniques). In an example, the intraencoder (622) also calculates intra prediction results (e.g., predictedblock) based on the intra prediction information and reference blocks inthe same picture.

The general controller (621) is configured to determine general controldata and control other components of the video encoder (603) based onthe general control data. In an example, the general controller (621)determines the mode of the block, and provides a control signal to theswitch (626) based on the mode. For example, when the mode is the intramode, the general controller (621) controls the switch (626) to selectthe intra mode result for use by the residue calculator (623), andcontrols the entropy encoder (625) to select the intra predictioninformation and include the intra prediction information in thebitstream; and when the mode is the inter mode, the general controller(621) controls the switch (626) to select the inter prediction resultfor use by the residue calculator (623), and controls the entropyencoder (625) to select the inter prediction information and include theinter prediction information in the bitstream.

The residue calculator (623) is configured to calculate a difference(residue data) between the received block and prediction resultsselected from the intra encoder (622) or the inter encoder (630). Theresidue encoder (624) is configured to operate based on the residue datato encode the residue data to generate the transform coefficients. In anexample, the residue encoder (624) is configured to convert the residuedata from a spatial domain to a frequency domain, and generate thetransform coefficients. The transform coefficients are then subject toquantization processing to obtain quantized transform coefficients. Invarious embodiments, the video encoder (603) also includes a residuedecoder (628). The residue decoder (628) is configured to performinverse-transform, and generate the decoded residue data. The decodedresidue data can be suitably used by the intra encoder (622) and theinter encoder (630). For example, the inter encoder (630) can generatedecoded blocks based on the decoded residue data and inter predictioninformation, and the intra encoder (622) can generate decoded blocksbased on the decoded residue data and the intra prediction information.The decoded blocks are suitably processed to generate decoded picturesand the decoded pictures can be buffered in a memory circuit (not shown)and used as reference pictures in some examples.

The entropy encoder (625) is configured to format the bitstream toinclude the encoded block. The entropy encoder (625) is configured toinclude various information according to a suitable standard, such asthe HEVC standard. In an example, the entropy encoder (625) isconfigured to include the general control data, the selected predictioninformation (e.g., intra prediction information or inter predictioninformation), the residue information, and other suitable information inthe bitstream. Note that, according to the disclosed subject matter,when coding a block in the merge submode of either inter mode orbi-prediction mode, there is no residue information.

FIG. 7 shows a diagram of a video decoder (710) according to anotherembodiment of the disclosure. The video decoder (710) is configured toreceive coded pictures that are part of a coded video sequence, anddecode the coded pictures to generate reconstructed pictures. In anexample, the video decoder (710) is used in the place of the videodecoder (310) in the FIG. 3 example.

In the FIG. 7 example, the video decoder (710) includes an entropydecoder (771), an inter decoder (780), a residue decoder (773), areconstruction module (774), and an intra decoder (772) coupled togetheras shown in FIG. 7.

The entropy decoder (771) can be configured to reconstruct, from thecoded picture, certain symbols that represent the syntax elements ofwhich the coded picture is made up. Such symbols can include, forexample, the mode in which a block is coded (such as, for example, intramode, inter mode, bi-predicted mode, the latter two in merge submode oranother submode), prediction information (such as, for example, intraprediction information or inter prediction information) that canidentify certain sample or metadata that is used for prediction by theintra decoder (772) or the inter decoder (780), respectively, residualinformation in the form of, for example, quantized transformcoefficients, and the like. In an example, when the prediction mode isinter or bi-predicted mode, the inter prediction information is providedto the inter decoder (780); and when the prediction type is the intraprediction type, the intra prediction information is provided to theintra decoder (772). The residual information can be subject to inversequantization and is provided to the residue decoder (773).

The inter decoder (780) is configured to receive the inter predictioninformation, and generate inter prediction results based on the interprediction information.

The intra decoder (772) is configured to receive the intra predictioninformation, and generate prediction results based on the intraprediction information.

The residue decoder (773) is configured to perform inverse quantizationto extract de-quantized transform coefficients, and process thede-quantized transform coefficients to convert the residual from thefrequency domain to the spatial domain. The residue decoder (773) mayalso require certain control information (to include the QuantizerParameter (QP)), and that information may be provided by the entropydecoder (771) (data path not depicted as this may be low volume controlinformation only).

The reconstruction module (774) is configured to combine, in the spatialdomain, the residual as output by the residue decoder (773) and theprediction results (as output by the inter or intra prediction modulesas the case may be) to form a reconstructed block, that may be part ofthe reconstructed picture, which in turn may be part of thereconstructed video. It is noted that other suitable operations, such asa deblocking operation and the like, can be performed to improve thevisual quality.

It is noted that the video encoders (303), (503), and (603), and thevideo decoders (310), (410), and (710) can be implemented using anysuitable technique. In an embodiment, the video encoders (303), (503),and (603), and the video decoders (310), (410), and (710) can beimplemented using one or more integrated circuits. In anotherembodiment, the video encoders (303), (503), and (603), and the videodecoders (310), (410), and (710) can be implemented using one or moreprocessors that execute software instructions.

In general, parallel processing can help to speed up computations and/orreduce hardware cost in a video codec. However, for a merge mode in somerelated technologies, a current coding block and a previous coding blockcannot be processed in parallel since the previous coding block may beused as a spatial merge candidate to predict the current block. Thisdisclosure presents improvement techniques for parallel processing in amerge mode.

According to a coding unit (CU) split tree, a coding region, such as acoding tree unit (CTU) can include a plurality of coding sub-regions,such as coding blocks (CBs) or sub-blocks. According to aspects of thedisclosure, a merge list can be shared for the coding sub-regionsincluded in the coding region when the coding region meets certainconditions. Such a merge list can be referred to as shared merge list.Accordingly, an ancestor node of the coding region, that is, a parentnode of the coding sub-regions, can be referred to as merge sharingnode, at which the shared merging list for the coding region isgenerated.

FIG. 8 shows four examples of merge sharing nodes according toembodiments of the disclosure. Each merge sharing node is indicated by arespective dotted virtual CU (801-804). As described above, in order tobe considered as a merge sharing node for a coding region, an ancestornode of the coding region should meet certain conditions, for example,when a size of the coding region is equal to or smaller than a sizethreshold. In the FIG. 8 examples, the size threshold is set to 64samples. Accordingly, the merge sharing node (801) includes four 4×4samples of blocks, each of the merge sharing nodes (802-803) includestwo 4×8 samples of blocks, and the merge sharing node (804) includes two4×4 samples of blocks and one 4×8 samples of block.

According to aspects of the disclosure, there are two types (Type-1 andType-2) of definitions for merge sharing nodes. According to Type-1definition, when a size of an ancestor node (e.g., a coding region) isequal to or smaller than a first size threshold, the ancestor node canbe considered as Type-1 merge sharing node. That is, a size of a parentnode of the ancestor node has to be larger than the first sizethreshold. According to Type-2 definition, an ancestor node can beconsidered as Type-2 merge sharing node when the ancestor node meets thefollowing two conditions: (1) a size of the ancestor node is equal to orlarger than a second size threshold; and (2) a size of one of childcodes of the ancestor node is smaller than the second size threshold. Itis noted that the first size threshold can be the same as the secondsize threshold in some embodiments.

According to aspects of the disclosure, the use of Type-1 or Type-2definition can be indicated in prediction information in an embodiment,or can be predefined in another embodiment. In addition, for each CUinside a CTU, a respective merge sharing node can be determined during aparsing stage of a decoding process. This rule may apply to both typesof merge sharing nodes.

FIG. 9 shows an example of a difference between Type-1 and Type-2definitions according to an embodiment of the disclosure. In the FIG. 9example, a coding region (900) with a size of 128 samples isternary-split into three child CUs (901-903), in which both child CUs(901 and 903) have a size of 8×4 samples, and the child CU (902) has asize of 8×8 samples. When Type-1 definition is applied to the codingregion (900) and the threshold is set to 64 samples, each of the threechild CUs (901-903) can have a respective merge sharing node. WhenType-2 definition is applied to the coding region (900) and thethreshold is set to 128 samples, the coding region (900) can have asingle merge sharing node and the three child CUs (901-903) can sharethe single merge list.

According to aspects of the disclosure, the shared merging list canapply to translational merge modes (e.g., HEVC/VVC merge modes, trianglemerge mode, and history-based merge candidate, etc.) and subblock-basedmerge modes (e.g., affine merge mode). For various merge modes, methodsof using the shared merging list can be similar in that the sharedmerging list is generated at the merge sharing node, given that themerge sharing node itself is considered as a child CU.

In some related technologies, all samples of a merge sharing node haveto be inside a picture boundary of a current picture regardless ofwhether the merge sharing node is Type-1 or Type-2. That is, when asample of an ancestor node is outside the picture boundary, thisancestor node cannot be considered as either Type-1 or Type-2 mergesharing node. Accordingly, if the ancestor node has a plurality of childnodes, at least one of the child nodes will be checked for determiningthe merge sharing node.

This disclosure presents improvement techniques for applying a sharedmerge list to a coding region that is partially located outside apicture boundary.

The methods present in the disclosure may be used separately or combinedin any order. Further, each of the methods (or embodiments), encoderand/or decoder may be implemented by processing circuitry (e.g., one ormore processors or one or more integrated circuits). In one example, theone or more processors execute a program that is stored in anon-transitory computer-readable medium. In the present methods, theterm block may be interpreted as a prediction block, a coding block, ora coding unit.

According to aspects of the disclosure, when a coding region ispartially located outside a picture boundary of a current picture, ashared merge list can still be applied to the coding region. That is, acommon merge candidate list can be derived for all sub-regions (e.g.,blocks or sub-blocks) inside the coding region, when the coding regionmeets some certain requirements.

In an embodiment, when a size of a coding region is equal to or smallerthan a first size threshold (e.g., 32 or 64 samples), a shared mergelist can be applied to the coding region. In another embodiment, when asize of a coding region is equal to or larger than a second sizethreshold, and a size of one of child CUs of the coding region issmaller than the second size threshold, a shared merge list can beapplied to the coding region. It is noted that the first size thresholdcan be the same as the second size threshold.

According to aspects of the disclosure, a shared merge list of a codingregion can include a temporal motion vector predictor (TMVP). In somerelated techniques, as described in the background section and shown inFIG. 1D, the TMVP can be derived from either a bottom-right cornerposition C0 or a center position C1 of a collocated block of the codingregion. The collocated block is in a reference picture of the codingregion. In some embodiments, C1 position is checked when the TMVP fromC0 position is invalid. However, when the coding region is partiallylocated outside a picture boundary of a current picture, it is possiblethat C1 position of the collocated block is also outside a pictureboundary of the reference picture.

Accordingly, this disclosure also presents some improvement techniquesfor the derivation of a TMVP in the shared merge list. In an embodiment,when deriving a TMVP from C1 position, the existence of C1 position ofthe collocated block is checked, in addition to checking whether the MVfrom this position is coded in inter mode or not.

In another embodiment, as shown in FIG. 10, when deriving a TMVP from C0position (1001) fails, instead of checking C1 position (1002), C2position (1003) is checked, which is adjacent a top-left corner of thecollocated block (1000). Since the top-left corner of the collocatedblock is always inside the picture boundary, the availability check ofC2 position is not necessary. Instead, the prediction mode check of C2position (1003) is still applied. That is, it is determined that whetheror not the MV from C2 position (1003) is coded in an inter prediction.

According to aspects of the disclosure, for a TMVP derivation process,C1 position is moved from the center location of the collocated block tothe top-left corner of the collocated block, regardless of whether theTMVP derivation process applies to a shared merge list or not. That is,when the TMVP from the bottom-right corner of the collocated block isinvalid, the TMVP from the top-left corner of the collocated blockinstead of the center location is checked in some embodiments.

FIG. 11 shows a flow chart outlining an exemplary process (1100)according to an embodiment of the disclosure. In various embodiments,the process (1100) is executed by processing circuitry, such as theprocessing circuitry in the terminal devices (210), (220), (230) and(240), the processing circuitry that performs functions of the videoencoder (303), the processing circuitry that performs functions of thevideo decoder (310), the processing circuitry that performs functions ofthe video decoder (410), the processing circuitry that performsfunctions of the intra prediction module (452), the processing circuitrythat performs functions of the video encoder (503), the processingcircuitry that performs functions of the predictor (535), the processingcircuitry that performs functions of the intra encoder (622), theprocessing circuitry that performs functions of the intra decoder (772),and the like. In some embodiments, the process (1100) is implemented insoftware instructions, thus when the processing circuitry executes thesoftware instructions, the processing circuitry performs the process(1100).

The process (1100) may generally start at step (S1101), where theprocess (1100) decodes prediction information for a coding region thatis partially located outside a picture boundary in a current picturethat is a part of a coded video sequence. Then the process (1100)proceeds to step (S1102).

At step (S1102), the process (1100) determines whether a shared mergelist is used for the coding region. When the shared merge list isdetermined to be used for the coding region, the process (1100) proceedsto step (S1103).

At step (S1103), the process (1100) constructs the shared merge list.Then the process proceeds to step (S1104).

At step (S1104), the process (1100) reconstructs the coding region basedon the shared merge list.

After reconstructing the coding region, the process (1100) terminates.

In an embodiment, the shared merge list is determined to be used for thecoding region when a size of the coding region is equal to or smallerthan a first size threshold.

In another embodiment, the coding region includes a plurality of codingblocks and the shared merge list is determined to be used for the codingregion when: (i) a size of the coding region is equal to or larger thana second size threshold; and (ii) a block size of one of the codingblocks is smaller than the second size threshold.

In an embodiment, the process (1100) selects a first block that islocated adjacent a center position of a collocated region of the codingregion. The collocated region is in a reference picture of the codingregion. Then the process (1100) determines whether the first block islocated inside the picture boundary of the current picture and is codedin an inter prediction mode. When the first block is determined to belocated inside the picture boundary of the current picture and to becoded in the inter prediction mode, the process (1100) constructs theshared merge list based on the first block.

In another embodiment, the process (1100) selects a second block that islocated adjacent a top-left position of the collocated region of thecurrent region. Then the process (1100) determines whether the secondblock is coded in an inter prediction mode. When the second block iscoded in the inter prediction mode, the process (1100) constructs theshared merge list based on the second block.

FIG. 12 shows a flow chart outlining an exemplary process (1200)according to another embodiment of the disclosure. In variousembodiments, the process (1200) is executed by processing circuitry,such as the processing circuitry in the terminal devices (210), (220),(230) and (240), the processing circuitry that performs functions of thevideo encoder (303), the processing circuitry that performs functions ofthe video decoder (310), the processing circuitry that performsfunctions of the video decoder (410), the processing circuitry thatperforms functions of the intra prediction module (452), the processingcircuitry that performs functions of the video encoder (503), theprocessing circuitry that performs functions of the predictor (535), theprocessing circuitry that performs functions of the intra encoder (622),the processing circuitry that performs functions of the intra decoder(772), and the like. In some embodiments, the process (1200) isimplemented in software instructions, thus when the processing circuitryexecutes the software instructions, the processing circuitry performsthe process (1200).

The process (1200) may generally start at step (S1201), where theprocess (1200) decodes prediction information for a current block in acurrent coded picture that is a part of a coded video sequence. Theprediction information indicates a merge mode for the current block.Then the process (1200) proceeds to step (S1202).

At step (S1202), the process (1200) examines a plurality of codingblocks of a collocated block of the current block according to anexamination order. A second examined position in the examination orderis one of the coding blocks that is located adjacent a top-left cornerof the collocated block. The collocated block is in a reference pictureof the current block. Then process (1200) proceeds to step (S1203).

At step (S1203), the process (1200) determines a temporal motion vectorpredictor (TMVP) according to the examined coding blocks. Then theprocess (1200) proceeds to step (S1204).

At step (S1204), the process (1200) reconstructs the current block basedon the TMVP.

After reconstructing the current block, the process (1200) terminates.

In an embodiment, the process (1200) selects one of the coding blocksaccording to the examination order and determines whether the selectedcoding block is coded in an inter prediction mode. When the selectedcoding block is determined to be coded in the inter prediction mode, theprocess (1200) includes a TMVP from the selected coding block into amerge list and reconstructs the current block based on the merge list.

In an embodiment, the coding block that is located adjacent the top-leftcorner of the collocated block is examined after a coding block that islocated adjacent a bottom-right corner of the collocated block accordingto the examination order.

The techniques described above, can be implemented as computer softwareusing computer-readable instructions and physically stored in one ormore computer-readable media. For example, FIG. 13 shows a computersystem (1300) suitable for implementing certain embodiments of thedisclosed subject matter.

The computer software can be coded using any suitable machine code orcomputer language, that may be subject to assembly, compilation,linking, or like mechanisms to create code comprising instructions thatcan be executed directly, or through interpretation, micro-codeexecution, and the like, by one or more computer central processingunits (CPUs), Graphics Processing Units (GPUs), and the like.

The instructions can be executed on various types of computers orcomponents thereof, including, for example, personal computers, tabletcomputers, servers, smartphones, gaming devices, internet of thingsdevices, and the like.

The components shown in FIG. 13 for computer system (1300) are exemplaryin nature and are not intended to suggest any limitation as to the scopeof use or functionality of the computer software implementingembodiments of the present disclosure. Neither should the configurationof components be interpreted as having any dependency or requirementrelating to any one or combination of components illustrated in theexemplary embodiment of a computer system (1300).

Computer system (1300) may include certain human interface inputdevices. Such a human interface input device may be responsive to inputby one or more human users through, for example, tactile input (such as:keystrokes, swipes, data glove movements), audio input (such as: voice,clapping), visual input (such as: gestures), olfactory input (notdepicted). The human interface devices can also be used to capturecertain media not necessarily directly related to conscious input by ahuman, such as audio (such as: speech, music, ambient sound), images(such as: scanned images, photographic images obtain from a still imagecamera), video (such as two-dimensional video, three-dimensional videoincluding stereoscopic video).

Input human interface devices may include one or more of (only one ofeach depicted): keyboard (1301), mouse (1302), trackpad (1303), touchscreen (1310), data-glove (not shown), joystick (1305), microphone(1306), scanner (1307), camera (1308).

Computer system (1300) may also include certain human interface outputdevices. Such human interface output devices may be stimulating thesenses of one or more human users through, for example, tactile output,sound, light, and smell/taste. Such human interface output devices mayinclude tactile output devices (for example tactile feedback by thetouch-screen (1310), data-glove (not shown), or joystick (1305), butthere can also be tactile feedback devices that do not serve as inputdevices), audio output devices (such as: speakers (1309), headphones(not depicted)), visual output devices (such as screens (1310) toinclude CRT screens, LCD screens, plasma screens, OLED screens, eachwith or without touch-screen input capability, each with or withouttactile feedback capability—some of which may be capable to output twodimensional visual output or more than three dimensional output throughmeans such as stereographic output; virtual-reality glasses (notdepicted), holographic displays and smoke tanks (not depicted)), andprinters (not depicted).

Computer system (1300) can also include human accessible storage devicesand their associated media such as optical media including CD/DVD ROM/RW(1320) with CD/DVD or the like media (1321), thumb-drive (1322),removable hard drive or solid state drive (1323), legacy magnetic mediasuch as tape and floppy disc (not depicted), specialized ROM/ASIC/PLDbased devices such as security dongles (not depicted), and the like.

Those skilled in the art should also understand that term “computerreadable media” as used in connection with the presently disclosedsubject matter does not encompass transmission media, carrier waves, orother transitory signals.

Computer system (1300) can also include an interface to one or morecommunication networks. Networks can for example be wireless, wireline,optical. Networks can further be local, wide-area, metropolitan,vehicular and industrial, real-time, delay-tolerant, and so on. Examplesof networks include local area networks such as Ethernet, wireless LANs,cellular networks to include GSM, 3G, 4G, 5G, LTE and the like, TVwireline or wireless wide area digital networks to include cable TV,satellite TV, and terrestrial broadcast TV, vehicular and industrial toinclude CANBus, and so forth. Certain networks commonly require externalnetwork interface adapters that attached to certain general purpose dataports or peripheral buses (1349) (such as, for example USB ports of thecomputer system (1300)); others are commonly integrated into the core ofthe computer system (1300) by attachment to a system bus as describedbelow (for example Ethernet interface into a PC computer system orcellular network interface into a smartphone computer system). Using anyof these networks, computer system (1300) can communicate with otherentities. Such communication can be uni-directional, receive only (forexample, broadcast TV), uni-directional send-only (for example CANbus tocertain CANbus devices), or bi-directional, for example to othercomputer systems using local or wide area digital networks. Certainprotocols and protocol stacks can be used on each of those networks andnetwork interfaces as described above.

Aforementioned human interface devices, human-accessible storagedevices, and network interfaces can be attached to a core (1340) of thecomputer system (1300).

The core (1340) can include one or more Central Processing Units (CPU)(1341), Graphics Processing Units (GPU) (1342), specialized programmableprocessing units in the form of Field Programmable Gate Areas (FPGA)(1343), hardware accelerators for certain tasks (1344), and so forth.These devices, along with Read-only memory (ROM) (1345), Random-accessmemory (1346), internal mass storage such as internal non-useraccessible hard drives, SSDs, and the like (1347), may be connectedthrough a system bus (1348). In some computer systems, the system bus(1348) can be accessible in the form of one or more physical plugs toenable extensions by additional CPUs, GPU, and the like. The peripheraldevices can be attached either directly to the core's system bus (1348),or through a peripheral bus (1349). Architectures for a peripheral businclude PCI, USB, and the like.

CPUs (1341), GPUs (1342), FPGAs (1343), and accelerators (1344) canexecute certain instructions that, in combination, can make up theaforementioned computer code. That computer code can be stored in ROM(1345) or RAM (1346). Transitional data can be also be stored in RAM(1346), whereas permanent data can be stored for example, in theinternal mass storage (1347). Fast storage and retrieve to any of thememory devices can be enabled through the use of cache memory, that canbe closely associated with one or more CPU (1341), GPU (1342), massstorage (1347), ROM (1345), RAM (1346), and the like.

The computer readable media can have computer code thereon forperforming various computer-implemented operations. The media andcomputer code can be those specially designed and constructed for thepurposes of the present disclosure, or they can be of the kind wellknown and available to those having skill in the computer software arts.

As an example and not by way of limitation, the computer system havingarchitecture (1300), and specifically the core (1340) can providefunctionality as a result of processor(s) (including CPUs, GPUs, FPGA,accelerators, and the like) executing software embodied in one or moretangible, computer-readable media. Such computer-readable media can bemedia associated with user-accessible mass storage as introduced above,as well as certain storage of the core (1340) that are of non-transitorynature, such as core-internal mass storage (1347) or ROM (1345). Thesoftware implementing various embodiments of the present disclosure canbe stored in such devices and executed by core (1340). Acomputer-readable medium can include one or more memory devices orchips, according to particular needs. The software can cause the core(1340) and specifically the processors therein (including CPU, GPU,FPGA, and the like) to execute particular processes or particular partsof particular processes described herein, including defining datastructures stored in RAM (1346) and modifying such data structuresaccording to the processes defined by the software. In addition or as analternative, the computer system can provide functionality as a resultof logic hardwired or otherwise embodied in a circuit (for example:accelerator (1344)), which can operate in place of or together withsoftware to execute particular processes or particular parts ofparticular processes described herein. Reference to software canencompass logic, and vice versa, where appropriate. Reference to acomputer-readable media can encompass a circuit (such as an integratedcircuit (IC)) storing software for execution, a circuit embodying logicfor execution, or both, where appropriate. The present disclosureencompasses any suitable combination of hardware and software.

While this disclosure has described several exemplary embodiments, thereare alterations, permutations, and various substitute equivalents, whichfall within the scope of the disclosure. It will thus be appreciatedthat those skilled in the art will be able to devise numerous systemsand methods which, although not explicitly shown or described herein,embody the principles of the disclosure and are thus within the spiritand scope thereof.

APPENDIX A: ACRONYMS

-   AMVP: Advanced Motion Vector Prediction-   ASIC: Application-Specific Integrated Circuit-   ATMVP: Alternative/Advanced Temporal Motion Vector Prediction-   BMS: Benchmark Set-   BV: Block Vector-   CANBus: Controller Area Network Bus-   CB: Coding Block-   CD: Compact Disc-   CPR: Current Picture Referencing-   CPUs: Central Processing Units-   CRT: Cathode Ray Tube-   CTBs: Coding Tree Blocks-   CTUs: Coding Tree Units-   CU: Coding Unit-   DPB: Decoder Picture Buffer-   DVD: Digital Video Disc-   FPGA: Field Programmable Gate Areas-   GOPs: Groups of Pictures-   GPUs: Graphics Processing Units-   GSM: Global System for Mobile communications-   HEVC: High Efficiency Video Coding-   HRD: Hypothetical Reference Decoder-   IBC: Intra Block Copy-   IC: Integrated Circuit-   JEM: Joint Exploration Model-   LAN: Local Area Network-   LCD: Liquid-Crystal Display-   LTE: Long-Term Evolution-   MV: Motion Vector-   OLED: Organic Light-Emitting Diode-   PBs: Prediction Blocks-   PCI: Peripheral Component Interconnect-   PLD: Programmable Logic Device-   PUs: Prediction Units-   RAM: Random Access Memory-   ROM: Read-Only Memory-   SCC: Screen Content Coding-   SEI: Supplementary Enhancement Information-   SNR: Signal Noise Ratio-   SSD: Solid-state Drive-   TUs: Transform Units-   USB: Universal Serial Bus-   VUI: Video Usability Information-   VVC: Versatile Video Coding

What is claimed is:
 1. A method for video decoding in a decoder,comprising: decoding prediction information for a coding region that ispartially located outside a picture boundary in a current picture thatis a part of a coded video sequence; determining whether a shared mergelist is used for the coding region; constructing the shared merge listresponsive to the shared merge list being used for the coding region;and reconstructing the coding region based on the shared merge list. 2.The method of claim 1, wherein the shared merge list is determined to beused for the coding region when a size of the coding region is equal toor smaller than a first size threshold.
 3. The method of claim 1,wherein the coding region includes a plurality of coding blocks and theshared merge list is determined to be used for the coding region when:(i) a size of the coding region is equal to or larger than a second sizethreshold; and (ii) a block size of one of the coding blocks is smallerthan the second size threshold.
 4. The method of claim 1, wherein theconstructing further comprises: selecting a first block that is locatedadjacent a center position of a collocated region of the coding region,the collocated region being in a reference picture of the coding region;and constructing the shared merge list based on the first block when thefirst block is located inside the picture boundary of the currentpicture and is coded in an inter prediction mode.
 5. The method of claim1, wherein the constructing further comprises: selecting a second blockthat is located adjacent a top-left position of the collocated region ofthe current region; and constructing the shared merge list based on thesecond block when the second block is coded in an inter prediction mode.6. A method for video decoding in a decoder, comprising: decodingprediction information for a current block in a current picture that isa part of a coded video sequence, the prediction information indicatinga merge mode for the current block; examining a plurality of codingblocks of a collocated block of the current block according to anexamination order, a second examined position in the examination orderbeing one of the coding blocks that is located adjacent to a top-leftcorner of the collocated block, and the collocated block being in areference picture of the current block; determining a temporal motionvector predictor (TMVP) according to the examined coding blocks; andreconstructing the current block based on the TMVP.
 7. The method ofclaim 6, wherein the examining further comprises: selecting one of thecoding blocks according to the examination order; and determiningwhether the selected coding block is coded in an inter prediction mode.8. The method of claim 6, wherein the coding block that is locatedadjacent the top-left corner of the collocated block is examined after acoding block that is located adjacent a bottom-right corner of thecollocated block according to the examination order.
 9. An apparatus,comprising a processing circuitry configured to: decode predictioninformation for a coding region that is partially located outside apicture boundary in a current picture that is a part of a coded videosequence; determine whether a shared merge list is used for the codingregion; construct the shared merge list responsive to the shared mergelist being used for the coding region; and reconstruct the coding regionbased on the shared merge list.
 10. The apparatus of claim 9, whereinthe shared merge list is determined to be used for the coding regionwhen a size of the coding region is equal to or smaller than a firstsize threshold.
 11. The apparatus of claim 9, wherein the coding regionincludes a plurality of coding blocks and the shared merge list isdetermined to be used for the coding region when: (i) a size of thecoding region is equal to or larger than a second size threshold; and(ii) a block size of one of the coding blocks is smaller than the secondsize threshold.
 12. The apparatus of claim 9, wherein the processingcircuitry is further configured to: select a first block that is locatedadjacent a center position of a collocated region of the coding region,the collocated region being in a reference picture of the coding region;and construct the shared merge list based on the first block when thefirst block is located inside the picture boundary of the currentpicture and is coded in an inter prediction mode.
 13. The apparatus ofclaim 9, wherein the processing circuitry is further configured to:selecting a second block that is located adjacent a top-left position ofthe collocated region of the current region; and constructing the sharedmerge list based on the second block when the second block is coded inan inter prediction mode.
 14. An apparatus, comprising a processingcircuitry configured to: decode prediction information for a currentblock in a current picture that is a part of a coded video sequence, theprediction information indicating a merge mode for the current block;examine a plurality of coding blocks of a collocated block of thecurrent block according to an examination order, a second examinedposition in the examination order being one of the coding blocks that islocated adjacent to a top-left corner of the collocated block, and thecollocated block being in a reference picture of the current block;determine a temporal motion vector predictor (TMVP) according to theexamined coding blocks; and reconstruct the current block based on theTMVP.
 15. A non-transitory computer-readable storage medium storing aprogram executable by at least one processor to perform: decodingprediction information for a coding region that is partially locatedoutside a picture boundary in a current picture that is a part of acoded video sequence; determining whether a shared merge list is usedfor the coding region; constructing the shared merge list responsive tothe shared merge list being used for the coding region; andreconstructing the coding region based on the shared merge list.
 16. Thenon-transitory computer-readable storage medium of claim 15, wherein theshared merge list is determined to be used for the coding region when asize of the coding region is equal to or smaller than a first sizethreshold.
 17. The non-transitory computer-readable storage medium ofclaim 15, wherein the coding region includes a plurality of codingblocks and the shared merge list is determined to be used for the codingregion when: (i) a size of the coding region is equal to or larger thana second size threshold; and (ii) a block size of one of the codingblocks is smaller than the second size threshold.
 18. The non-transitorycomputer-readable storage medium of claim 15, wherein the storingprogram is further to perform: selecting a first block that is locatedadjacent a center position of a collocated region of the coding region,the collocated region being in a reference picture of the coding region;and constructing the shared merge list based on the first block when thefirst block is located inside the picture boundary of the currentpicture and is coded in an inter prediction mode.
 19. The non-transitorycomputer-readable storage medium of claim 15, wherein the storingprogram is further to perform: selecting a second block that is locatedadjacent a top-left position of the collocated region of the currentregion; and constructing the shared merge list based on the second blockwhen the second block is coded in an inter prediction mode.
 20. Anon-transitory computer-readable storage medium storing a programexecutable by at least one processor to perform: decoding predictioninformation for a current block in a current picture that is a part of acoded video sequence, the prediction information indicating a merge modefor the current block; examining a plurality of coding blocks of acollocated block of the current block according to an examination order,a second examined position in the examination order being one of thecoding blocks that is located adjacent to a top-left corner of thecollocated block, and the collocated block being in a reference pictureof the current block; determining a temporal motion vector predictor(TMVP) according to the examined coding blocks; and reconstructing thecurrent block based on the TMVP.